Cement-based fire door core

ABSTRACT

The present invention describes an improved building material composition, useful for example as a fire door core. The building material of the present invention is prepared by compressing an aqueous mixture of expanded perlite and a fast setting, cementitious composition consisting essentially of a hydraulic cement, preferably Portland cement, and a pozzolan additive selected from the group consisting of metakaolin, VCAS and mixtures thereof, and preferably also includes an organic binder and a fibrous reinforcement.

TECHNICAL FIELD

This invention is in the field of building materials, especially fire-resistant building materials. Specifically, this invention describes a building material made from a particular fast setting cementitious composition and having utility as an improved core composition for fire doors.

BACKGROUND OF THE INVENTION

Fire doors are generally made for the purpose of stopping or delaying the transfer of thermal energy (i.e., heat), from one side of the door to the other side. Current fire-resistant doors generally contain a fire-resistant core usually encased in a door-shaped shell, wherein the shell is made from various materials generally known to those of ordinary skill in the art. The core is customarily bonded or glued to both inside surfaces of the shell.

Fire doors, as used in residential, commercial, and industrial applications, typically are employed in conjunction with fire walls to provide fire protection between different zones of a structure, and particularly to isolate high fire risk areas of a building from the remainder of the structure, such as the garage of a dwelling from its living quarters. Fire doors usually are not capable of indefinitely withstanding the high temperature conditions of a fire but, rather, are designed to maintain the integrity of the firewall for a limited time to permit the occupants of a building to escape and to delay the spread of fire until fire control equipment can be brought to the scene.

Various tests have been designed for fire doors and are based on factors, such as the time that a given door would withstand a certain temperature while maintaining its integrity, and hose stream tests which involve the door's ability to withstand the forces of a high pressure water stream. The American Society for Testing Materials (ASTM) has devised tests to establish fire door standards and these standards are incorporated into building codes and architectural specifications. One such standard, ASTM Method E 152, requires a door to maintain its integrity for period ranging up to 1.5 hours while withstanding progressively higher temperatures and erosive effects of a high pressure stream of water from a fire hose at the conclusion of the heat (fire) exposure.

Considerations in fire door design, in addition to retarding the advance of fire, include the cost of raw materials and the cost of fabrication. Furthermore, the weight of the door is important, both from the standpoint of ease of handling and cost of transportation. The strength of the door is also a significant factor, since fire doors must pass the above-described water stream test as well as have the requisite strength to withstand normal use and abuse.

Fire-resistant doors have been made using a variety of constructions and utilizing a number of different materials, including wood, metal, and mineral materials. Early forms of fire doors simply comprised wooden cores faced with metal sheeting. Although wood of ample thickness is an effective fire and heat retardant, doors of such construction tend to be heavy and are expensive to fabricate and transport.

Mineral fibers have also been employed in the manufacture of fire doors. The core of a commercial metal fire door principally comprises a composition including mineral fibers and a binder. Such doors suffer, however, from a lack of strength, and handling the friable cores results in the production of irritating dust particles during the manufacturing process.

Some fire-resistant cores are constructed using such materials as perlite (which functions as an inorganic filler), gypsum (which functions as the fire resistant material), cement (which functions as a further fire resistant material and counteracts shrinkage of the core), a solution of polyvinyl alcohol and water (which also acts as a binder and increases the viscosity of the mixture of ingredients while also hydrating the gypsum) and fiberglass (which functions as a reinforcing material). See for example U.S. Pat. No. 4,159,302, the disclosure of which is incorporated herein by reference.

It has also been proposed to make fire doors wherein the core comprises particles of expanded perlite, which are bound together by the use of various hydraulic binders including gypsum, cement, and inorganic adhesive material. In order to provide sufficient strength, particularly to withstand handling of the core during manufacture, the core typically is compressed to compact the mixture to a relatively high density, resulting in a heavy door.

Other fire doors have included conventional gypsum wallboard panels as a core material. However, in order to produce sufficient fire resistance, the thickness required of the wallboard is such as to result in an excessively heavy door. Furthermore, internal structural members such as rails or mullions have been found necessary to support and strengthen wallboard panels. The need for such reinforcing elements increases the cost of materials and assembly of such doors. In addition to the above-mentioned considerations, fire doors must, in order to be commercially acceptable, also have other properties that are related to the manufacture, installation and service of the fire door.

Fire door cores that contain a significant proportion of gypsum may lose their fire resistant capabilities in the course of a fire. As is well known, gypsum calcines when contacted with sustained heat. During a fire, calcination of the gypsum in a door core may cause the core to lose strength and integrity, especially when thereafter exposed to water, such as a high pressure stream of water from a hose. Thus, the fire resistance and structural integrity of such a door core is degraded. Furthermore, current fire-resistant door cores containing gypsum exhibit high water absorption rates thereby increasing both their size and density.

U.S. Pat. No. 6,340,389 describes a fire door cores made from expanded perlite, a fireproof binder such as an alkali metal silicate, fire clay or vermiculite, and optionally one or more viscosity-enhancing components, fiberglass, or both. The fire door core is made using a semi-continuous batch press method wherein water, the expanded perlite, the fireproof binder, fire clay or vermiculite are mixed; and the wet mixture is compressed in a mold, and the compressed mixture dried.

U.S. Pat. No. 6,846,358 describes an improved building material composition, useful for example as a fire door core and to improved methods of making this composition. The building material is prepared from an aqueous mixture of expanded perlite and a fast setting, cementitious composition consisting essentially of a hydraulic cement having (1) a Portland cement and (2) a calcium aluminate cement, which composition is molded and shaped into a fire door core.

There continues to be a demand for building materials suitable for use as fire door cores. In order to meet this commercial need, a door core should maintain its strength and integrity and have acceptable hose stream resistance after being exposed to heat. Additionally, to enhance its commercial viability the door core should be easily manufactured using techniques well-known in the art. The present invention fulfills these commercial needs by using an improved fast setting cementitious composition as the major structural component of the composition.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is directed to a building material composition which can be used as a fire door core. Building material compositions (e.g., fire door cores) of the present invention can meet and in some cases may exceed the fire-resistant capabilities of current fire door cores. One characterizing feature of the building material composition (e.g., fire door core) of the present invention is that it is substantially free of set gypsum. The building material composition (e.g., fire door core) of the present invention comprises, as its main constituent, an expanded perlite and as a second, normally minor, though essential constituent, a cured fast setting, cementitious composition. The ingredients used to prepare the building material composition, upon hydration with water, can be molded, shaped and cured into a desired shape, such as for a fire door core.

The fast setting cementitious composition of this invention consists essentially of a mixture of (1) a hydraulic cement component, and particularly a Portland cement (ordinary Portland cement or OPC) and (2) a pozzolan additive selected from the group consisting of metakaolin, a Vitreous Calcium Aluminosilicate (known as VCAS) and mixtures thereof. Upon being mixed with water in an amount within the range of about 15 to 50 percent by weight, more usually within the range of about 20 to 40 wt. %, and most often within the range of about 25 to 35 wt. %, based on the weight of the dry mixture of the constituents, the resulting moist composition exhibits a suitable setting time for manufacturing fire door cores.

The fire door core may also contain, as minor optional (though often preferred) components, an organic binder, most preferably polyvinyl alcohol (i.e., a polyvinyl acetate which is substantially fully hydrolyzed), and a fibrous reinforcement, most preferably chopped glass fibers.

Still other optional (minor) ingredients include an alkali metal silicate, unexpanded vermiculite, and clay.

Preferably, the hydraulic cement component and particularly a Portland cement (OPC), of the fast setting cementitious composition is present in a weight ratio relative to the pozzolan additive (PA), i.e., OPC:PA within the range of about 3:1 to 30:1 and more preferably, within the range of about 4:1 to 15:1.

The building material or fire door core composition of the present invention can be made by admixing the expanded perlite, the fast setting, cementitious composition, an optional organic binder, an optional fibrous reinforcement and other optional additives which may also be used, with an amount of water at least sufficient to provide a moist, (damp) mixture of the ingredients and sufficient to set the fast setting cementitious composition. Water preferably is added in an amount of between about 20 to 40 wt % of the weight of the dry ingredients in the composition. The composition can then be molded into the desired shape, including a desired thickness, and density for the fire door core.

DETAILED DESCRIPTION OF THE INVENTION

The building material composition, preferably in the form of a fire door core, of the present invention comprises as a major component expanded perlite and as a second, generally minor (though essential), component a cured fast setting cementitious composition which consists essentially of a mixture of (1) a hydraulic cement component, particularly Portland cement (OPC), and (2) a pozzolan additive selected from the group consisting of metakaolin, VCAS and mixtures thereof.

For convenience, the building material composition is typically defined in terms of its constituent components notwithstanding the fact that at least in the case of the two components of the fast setting cementitious composition there is understood to be a chemical interaction that occurs during the setting and curing of the composition as the final product is formed.

The main constituent of the fire door core of the present invention is an expanded perlite. Expanded perlite is present in the door core in an amount of about 65 to 85 weight percent based on the total weight of the other dry ingredients. Expanded perlite is available in various forms as is well known to those of ordinary skill in the art. Speaking generally, expanded perlite can be formed by heating moisture-containing, natural-occurring perlite ore at a temperature within the range of about 1,500° to 2,000° F. (815° to 1093° C.) Such heat treatment explodes or expands the perlite to, for example, 15-20 times its original volume. Commercially available forms of expanded perlite known as cryogenic, plaster and concrete aggregate are exemplary of materials that can be used in the practice of the present invention. Expanded perlite, suitable for use in the present invention, generally has a density from about 2 to about 11 lbs per cubic foot (pcf). Usually, an expanded perlite with a density of about 4 to 8 pcf will be used, particularly an expanded perlite such as a 6.5 pcf perlite. Furthermore, the particle size of the expanded perlite used in making the building material composition can vary over a wide range. Generally an expanded perlite having a particle size distribution that passes through a 30 mesh screen and is retained on a 100 mesh screen (U.S. Standard Sieve Series) should be suitable.

The expanded perlite functions as a non-combustible, compactable filler which imparts light weight to the set (cured) composition, and also relatively high strength as compared to other means which could be used to impart light weight to the set composition, for example, such as by introducing air voids into the set composition by foaming the mixture of ingredients from which the set composition is made.

To optimize strength properties of the core, those forms of expanded perlite which are more resistant to being compressed or compacted relative to other more compactable forms of perlite should preferably be used. It has been observed that various forms of perlite are less spongy than others. The less spongy the perlite, the greater its resistance to being compressed and the greater the anticipated strength of the core made from the perlite. Conversely, the more spongy the perlite, the more readily it is compressed and the lower the anticipated strength of the core. See U.S. Pat. No. 4,159,302 for additional discussion.

While generally present as a minor component of the building material composition, the set or cured fast setting cementitious component, which consists essentially of a mixture of (1) a hydraulic cement component, particularly a Portland cement (e.g., OPC), and (2) a pozzolan additive selected from the group consisting of metakaolin, VCAS and mixtures thereof, constitutes the principal constituent holding the building material composition together as a unitary construction. The fast setting cementitious composition is added to form the building material composition in an amount of 10 to 45 percent by weight, more usually within the range of about 15 to 40 wt. %, and most often within the range of about 18 to 30 wt. %, of the weight of the dry mixture of the constituents used to make the composition.

Portland cements represent a class of hydraulic cements that contain a substantial quantity of calcium silicate with only minor quantities of aluminates, namely, tricalcium aluminate and a calcium aluminoferrite. As known to those skilled in the art, Portland cements are produced by heating, to incipient fusion, an intimate mixture of calcareous and argillaceous, or other siliceous, aluminious, and iron-oxide-bearing materials so as to form a clinker. The clinker then is pulverized and a small amount of calcium sulphate, usually gypsum, is added to improve the setting characteristics of the finished cement.

Portland cements are commonly characterized by type in accordance with standards developed by the American Portland Cement Association and the standards and designations applied there are used in characterizing Portland cements herein (Types I, IA, II, IIA, I/II, III, IIIA, IV and V). The Portland cement constituent of the present invention can be anyone of these wide variety of Portland cement types, though the normal, general purpose Type I Portland cement (OPC) is usually suitable. As noted, such cements principally contain calcium silicate and have a relatively low alumina content, i.e., less than 10 wt. %. Portland cement compositions typically contain more than 60% CaO and less than 3% aluminum and 1.5% sulfur.

The second component of the fast setting cementitious component is a pozzolan additive selected from the group consisting of metakaolin, VCAS and mixtures thereof. These pozzolans are non-cementitious on their own, but react with calcium hydroxide produced during the hydration of a hydraulic cement, such as Portland cement, to form additional cementations compounds, such as calcium silicate hydrates and alumino-silicate hydrates, which fill in pores in the cured cement and densify the concrete matrix.

Metakaolin is a dehydroxylated form of kaolinite. Metakaolin is formed by heating (calcining) kaolinite (e.g., china clay or kaolin clay) between about 500 to 800° C., more usually between 650 to 700° C. The dehydoxylation that occurs at this temperature produces an amorphous, highly pozzolanic material. Highly reactive metakaolin is available from Advanced Cement Technologies, LLC, Blaine, Wash., USA and from BASF (previously Engelhard Corporation), New Jersey, USA.

VCAS (Vitreous Calcium Aluminosilicate) pozzolan is available from Vitro Minerals Inc, Canton Mich. and is produced from glass fiber manufacturing waste as described in U.S. Pat. No. 6,776,838. A molten blend of ground silica, lime and alumina compounds is solidified by quench cooling and ground to a fine white powder.

The hydraulic cement, e.g., Portland cement component (OPC) and the pozzolan additive selected from the group consisting of metakaolin, VCAS and mixtures thereof (PA) are present in the fast setting cementitious component of the building material composition in a weight ratio (OPC:PA) within the range of about 3:1 to 30:1 and more preferably, within the range of about 4:1 to 15:1. A preferred formulation includes Portland cement in a weight ratio to the pozzolan additive of about 10:1.

The set cementitious composition component imparts to the building material composition, such as to a fire door core, good water resistant properties and high compressive strength. Accordingly, the set cementitious composition helps to maintain the integrity of the fire door core when the door is exposed to the wetting and the pressure of a hose stream. In addition, the set cementitious composition functions as a shrink resistant material in the core when it is exposed to fire.

The building material composition, e.g., fire door core composition, of the present invention does not require set gypsum as a significant structural component and thereby avoids problems associated with current compositions used as door cores which rely primarily on set gypsum, i.e., the door core of the present invention is substantially free of set gypsum. In fact, the building material composition of this invention is preferably free from added gypsum altogether. Current door cores that contain gypsum cannot be considered fire-proof, at best, they can only be considered fire-resistant. Fire door cores, that contain gypsum as a structural component, have the problem that, when subjected to extended heating, the gypsum calcines and the door core loses its strength and integrity. Thus, when the door core thereafter is contacted by water, typically in the form of a high pressure stream of water from a hose, the integrity of the door is compromised because the calcined gypsum is washed away. The fire door core of the present invention is expected to meet or exceed the capabilities of current fire-resistant cores made with set gypsum in standard fire tests for residential and non-residential use. The fire door core of the present invention also is expected to exceed the capabilities of fire-resistant door cores containing set gypsum in maintaining strength and integrity following prolonged heat, even when exposed to water.

The building material composition, especially the fire door core, of the present invention can also optionally include, and preferably does contain, still additional components, particularly an organic binder and a fibrous reinforcement, to achieve desired flexural and compressive strength and general handling characteristics. While desired strength characteristics may be achieved without the use of the organic binder and fibrous reinforcement, the absence of these optional ingredients tends to increase the density of the product at an equivalent level of properties. Thus, use of an organic binder and fibrous reinforcement are often preferred.

The organic binder is preferably a synthetic material such as polyvinyl alcohol, polyvinyl acetate, polymers of vinyl acetate and ethylene, polymers of styrene and butadiene, and acrylic resins.

The organic binder is typically a material which is dispersible or soluble in water. Indeed, in many cases the organic binder will be introduced into the mixture of ingredients used to form the building material composition as an aqueous solution or as an aqueous dispersion during the preparation of the building material composition, with the water introduced with the organic binder supplying a portion of the water required by the process for making the ultimate product, i.e., for hydrating the fast setting cementitious component as the composition sets and cures.

A preferred organic binder is polyvinyl alcohol, a well known commercially available water soluble material. Speaking generally, polyvinyl alcohol is prepared by hydrolyzing polyvinyl acetate. The source of the polyvinyl alcohol is preferably a substantially completely hydrolyzed form of polyvinyl acetate, that is, about 97 to 100% hydrolyzed polyvinyl acetate. A suitable polyvinyl alcohol can be cold-water insoluble. In this case, solutions can be prepared at elevated temperatures, for example, at temperatures of about 140° to 205° F. (60° to 96° C.). Commercially available polyvinyl alcohols for use in the composition of the present invention are available from the Dupont Company under the trademark “Elvanol.” Examples of such products are Elvanol, Grades 90-50, 71-30, 75-15, 72-60 and 70-06. When used, the organic binder is generally included in the building material composition in an amount of up to about 5 percent by weight, such as from 1 to 5 percent, usually about 3 percent or less, such as from 1 to 2 percent, each of these percents based on the total weight of the dry ingredients used to form the building material composition, e.g., the fire door core.

The fibrous reinforcement also imparts flexibility and impact-resistant properties to the set composition, and also provides better handling properties to improve resistance to cracking or breakage during shipment or processing of the door core. As fibrous reinforcements glass fibers are preferred. Examples of other fibrous reinforcements that can be substituted for glass fibers or used in combination therewith are mineral fibers (such as Wollastonite and mineral wool), sisal fibers, graphite fibers, and synthetic fibers such as, for example, polyolefin fibers, such as polyethylene fibers and polypropylene fibers, rayon fiber and polyacrylonitrile fiber. The fiber reinforcement also may improve the material handling properties of the wet mixture, e.g., the wet door core mixture and especially the wet composite, e.g., the wet door core. Typically, when used, the amount of fiber reinforcement is no more than about 2 percent by weight, such as from 0.1 to 2 percent, usually about 1 percent or less, such as from 0.2 to 1 percent, more usually, from about 0.2 to about 0.7 percent, each of these percents based on the total dry weight of the various ingredients used to form the building material composition, e.g., the fire door core.

Still other optional ingredients also may be included in the mixture of ingredients used to prepare the building material composition or fire door core, such as unexpanded verimculite (to enhance fire resistant properties of the set composition and to counteract any tendency to shrink at elevated temperatures thereby imparting improved dimensional stability properties to the set composition during exposure to heat), clay (to improve fire resistant and high temperature, dimensional stability properties), and possibly a defoamer. These optional additional ingredients do not prevent the composition from fulfilling, and in most cases enhance, its use in fire resistant applications.

Clays are natural, earthy, fine-grained materials, most of which exhibit plastic characteristics when moistened with limited amounts of water. In general, clays comprise primarily alumina, silica and water and may also contain to a lesser extent iron, alkali, alkaline earth and other metals. The various types of clays in general have particles ranging in size from fractions of a micron to about 40 microns, although some materials having particles of an even larger size are also considered clays. It should be understood that materials which do not have all of the above characteristics, but which nevertheless are generally referred to as clays because they have one or more of the above characteristics are included within the term “clay” as used herein. Examples of the types of clay that can optionally be utilized are: kaolinitic clays—including, for example, kaolin (also referred to as china or paper clays), ball clay, fireclay, and flint clay, which clays are comprised predominantly of the clay mineral kaolinite.

The building material composition when used as a fire door core in accordance with the present invention is expected to provide several advantages over currently used fire-resistant door cores, including but not limited to, increased production capabilities using methods known to those of ordinary skill, decreased raw material consumption, stronger adhesion to door shells, sufficient thermal integrity to allow use of thermosetting binders for attaching door skins, increased tensile and flexural strength, superior hose stream resistance, decreased weight, and better shaping and handling characteristics.

The phrase “consisting essentially of” when used in connection with the present invention and in the claims is intended to exclude not only the use of ingredients that would destroy the fire resistant property of the composition, but also to exclude the addition of calcined gypsum in amounts in excess of about 5% by weight. Preferably, calcined gypsum is not added to the mixture of ingredients used to form the composition in excess of about 2% by weight.

As to amounts of ingredients preferably utilized in the practice of the present invention, the set building material composition comprises the set product of an aqueous mixture, based on the total dry weight of the ingredients used in the mixture, of:

-   -   (A) about 65 to about 85 wt. % of expanded perlite;     -   (B) about 15 to about 50 wt. % of the fast setting cementitious         component;     -   (C) up to 5% and preferably about 1 to about 5 wt. % of an         organic binder;     -   (D) up to about 2 wt. % and preferably about 1% of fibrous         reinforcements,     -   (E) 0 to about 4 wt. % of clay; and     -   (F) 0 to about 4 wt. % of unexpanded vermiculite.

In a more preferred form, the aforementioned aqueous mixture includes, based on the total dry weight of the various ingredients in the mixture:

-   -   (A) about 65 to about 85 wt. % perlite;     -   (B) about 20 to about 40 wt. % of the fast setting cementitious         component;     -   (C) at least about 1.5 wt. % of an organic binder;     -   (D) at least about 0.2 wt. % and up to 1% of a fibrous         reinforcement     -   (E) 0 to about 4 wt. % of unexpanded vermiculite; and     -   (F) 0 to about 4 wt. % of clay.

The building material composition, e.g., a fire door core, of the present invention is manufactured by combining the various components (most of which are generally supplied as dry ingredients) with water to form a wet mixture, e.g., a wet door core mixture. The amount of water to use in making a set composition, e.g., a door core, is at least sufficient to provide the stoichiometric amount of water needed to cause the setting (curing) of the fast setting cementitious component. It is generally desirable to include an amount of water in excess of the stoichiometric amount. In certain embodiments, it may be preferred to use only an amount of water sufficient to provide a damp (moist) mixture of the ingredients. In alternative embodiments, higher amounts of water can be used, for example, amounts that produce a moldable slurry of the dry, solid ingredients. In most cases, a set composition, such as a door core, can be prepared readily using from about 15 to about 60% by weight of water based on the dry weight of the various ingredients comprising the mixture. Usually an amount of water in the range of about 15 to 45 wt. %, more usually within the range of 20 to 40 wt. %, of the dry weight of the mixture of ingredients, should be suitable for preparing the wet composition, e.g., a wet door core mixture.

The wet mixture, e.g., the wet door core mixture, then is molded and pressed as needed to form a wet composite, e.g., a wet door core. The wet composite, e.g., wet door core, then is dried to form the building material composition, e.g., the fire door core, of the invention.

As described herein, the wet mixture, e.g., the wet door core mixture, and the wet composite, e.g., wet door core, preferably have a solids concentrations, that provide ease of handling, i.e., the solids concentrations are not so high as to cause difficulty in the mixing and/or transferring of the wet mixture from mixer to mold, and is not so low as to yield a wet composite, e.g., a wet door core, that lacks dimensional stability. Therefore, the form, i.e., whether as a dry solid or as an aqueous mixture, of an individual component used in preparing the mixture from which the building material composition is prepared, typically is selected so that the solids concentration of the wet mixture, e.g., the wet door core mixture and the wet composite, e.g., the wet door core, need not be adjusted. However, additional water may be added to obtain a wet mixture, e.g., a wet door core mixture and then a wet composite, e.g., a wet door core, having a desired handling property, if necessary.

An alkali metal silicate can also be used as an optional ingredient in the mixture for forming the building material composition. The alkali metal silicate can be used in an amount of from 0% up to about 15 percent of the total dry weight of the mixture of ingredients used to prepare the composition, e.g., of the fire door core. Preferably, the alkali metal silicate is sodium silicate or potassium silicate, more preferably it is sodium silicate. Sodium silicate used in the fire door core of the invention typically has a molar ratio of silica to sodium oxide of from about 2.5:1 to about 4:1. Preferably, the ratio of silica to sodium oxide is about 3.22:1. When used, the sodium silicate is provided to the mixture generally as an aqueous solution. The solids concentration in this aqueous silicate solution (along with any additional water used to make the wet mixture of ingredients for forming the fire door composition) must yield a wet composite, e.g., a wet door core, that is easy to handle, both during molding operations and after the wet composite, e.g., the wet door core, is removed from the mold, and is economically dried.

Typically, the solids content of sodium silicate solution optionally used in this invention is between about 30 and about 50 weight percent, more usually between about 34 and 44 weight percent, and most often about 37 weight percent solids. Silicate solutions having lower or higher solids concentrations also can be used. A commercial example of a solution of sodium silicate and water is ‘N’ grade sodium silicate solution marketed by PQ Corporation of Valley Forge, Pa. This solution has a molar ratio of silica to sodium oxide of 3.22:1 and a solids concentration of 37 weight percent.

Optionally, one or more dispersing agents or plasticizers can be used in combination with the optional alkali silicate additive for producing the building material composition, e.g., the fire door core, of the present invention to facilitate processing of the wet mixture. Specific concentrations, amounts, and identity of the optional dispersing agent or plasticizer will be apparent to skilled practitioners who recognize that these parameters will vary depending on external preferences such as price and availability of the additional components and that the described embodiments do not limit the scope of the claimed invention.

Use of a dispersing agent or plasticizer also may enhance certain physical properties of the building material composition, e.g., certain properties of the fire door core, such as flexibility and toughness. It may be possible to use inexpensive plasticizers such as sugar and sorbitol. Such other materials will be readily recognized by those skilled in the art and are commercially available from a number of suppliers.

A plasticizer, if used, would also generally be added to the formulation in an amount of about 0.1 to 4 wt. percent, more usually about 1 to 2 wt. percent, of the total weight of the building material composition (that is percent by weight of the dry solids used in forming the composition).

The building material composition, e.g., the fire door core of the present invention may contain still other optional components as long as these other components do not adversely affect the advantageous properties, especially the fire resistant property, of the composition, e.g., the fire resistant property of the fire door core, of the present invention. For example, another optional ingredient is diatomaceous earth. Diatomaceous earth is predominately silica and is composed of the skeletal remains of small prehistoric aquatic plants related to algae (diatoms). Particles of diatomaceous earth typically have intricate geometric forms. The irregular particle shapes are believed to improve the overall binding of the composition together and the resultant strength of the composition. Generally, the amount of such other optional components, such as the diatomaceous earth is less than about 10 weight percent of the building material composition, e.g., the fire door core. In the case of the diatomaceous earth in particular, when used the diatomaceous earth will generally be used in an amount of from about 1 to 10 weight percent, more usually from about 2 to about 8 weight percent and most often from about 3 to about 6 weight percent of the building material composition, e.g., the fire door core. The amount of these optional components is preferably less than about 10 weight percent, even more preferably the amount is less than about 5 weight percent.

The continuous roll press method is one known process of making the building material composition of the present invention and especially fire door cores. Illustrative of the known roll method is the method described in U.S. Pat. No. 5,256,222, the disclosure of which is incorporated herein by reference. A non-solid (aqueous) mixture of the components of the composition, e.g., fire door core, is deposited onto a moving web drawn from a supply roll by pull rolls. Then, another moving web drawn from its own supply roll by pull rolls is directed by guide and press roll(s) onto the top of the mixture. The thickness of the sandwich of fire door core mixture and webbing then is reduced to a desired value by roll-pressing. The roll molded fire door core then is transported by known industrial methods to a drying area (such as an oven). The drying of the roll molded fire door core can be achieved at ambient temperature or by using drying equipment that operates at a temperature greater than room temperature.

In accordance with a semi-continuous batch press mold method, the ingredients of the building material composition, e.g., the fire door core and water, are mixed in a suitable mixing device to produce the wet mixture, e.g., the wet door core mixture. Mixing devices suitably used in this step of the process are well known to skilled practitioners. Preferably, the dry ingredients are mixed with an amount of water no greater than that required to provide a damp (moist) mixture of the ingredients and then the moist (damp) mixture is then molded and compressed to form the composition or core as described below. It is preferred that the ingredients of the composition, e.g., the fire door core ingredients, be mixed in a manner such that the expanded perlite is substantially unbroken. In order to substantially eliminate the breaking of the expanded perlite during mixing, preferably the other components of the composition, e.g., the other fire door core ingredients, are mixed together first. This allows the expanded perlite to thoroughly blend with the other ingredients with a minimum of mixing. The amount of expanded perlite broken during the mixing process can be determined by comparing the volume of the wet mixture, e.g., the wet door core mixture before and after mixing.

The wet mixture, e.g., the wet door core mixture then is transferred to a mold having a shape corresponding to desired composite dimensions. Typically, a door core is molded to form a slab having the dimensions 36″×84″×1¾″. The moist mixture transfer step can be accomplished using any of the techniques well known to skilled practitioners. The wet mixture, e.g., the wet door core mixture then is compression molded to compact the mixture to the desired density and thickness to produce a wet composite, e.g., a wet door core.

The press molding of the present invention can use any means of pressure well known to those of skilled practitioners and suitable equipment is well known to the skilled worker. Typically, the level and the duration of the applied pressure is sufficient to bind the ingredients together in a composition, e.g., in a door core, that has a density from about 18 to about 35 pounds per cubic foot, more usually between about 23 to about 28 pounds per cubic foot, after drying, while at the same time being insufficient to break a significant number of the expanded perlite particles. It is expected that satisfactory results will be obtained by compressing the damp mixture to about 25 to about 33% of its original volume, utilizing pressures within the range of about 90 to about 170 psi for about 15 to about 55 seconds, and more usually about 100 to 130 psi. As skilled practitioners will recognize the exact pressure and time required will vary for different embodiments of the present invention and suitable pressure and time schedules can be determined using routine testing. The wet composite, e.g., the wet door core then is transferred to a drying area.

The wet composite, e.g., wet door core, then is dried (cured) to produce the building material composition, e.g., the fire door core of the present invention. The wet composite, e.g., the wet door core is cured (i.e., dried) at a temperature and for a time sufficient to substantially eliminate excess water from the wet composite, e.g., from the wet door core. Although the drying can be accomplished at ambient temperature, drying at elevated temperatures may often be preferred. For example, drying of the wet composite, e.g., the wet door core, may be carried out at a temperature from about 150° to about 300° Fahrenheit (about 65° to 150° C.), for a time from about 4 to about 8 hours, with lower temperatures requiring longer times. Skilled practitioners recognize that specific curing times and temperatures will depend on the exact composition of the wet composite, e.g., the wet door core and suitable temperature and time schedules can be determined using routine testing.

After the core has been dried, finishing operations can be effected. For example, the core can be sanded to a thickness within the required tolerance, sawed or shaped as desired. The nature of the dried material is such that finishing operations can be performed readily.

During the course of finishing operations such as sanding and sawing, core dust is produced. In accordance with this invention, it is anticipated that the dust can be used in preparing other cores by including it in the mixture from which the core is made. This is advantageous because it makes use of a material that would otherwise be waste requiring disposal. The use of core dust is expected to increase the density of the core. Accordingly, the maximum amount of core dust used will be governed by the desired density of the core. It is recommended that the core dust comprise no more than about 6 wt. % of the total weight of the dry mixture of ingredients. Preferably, the core dust should comprise no more that about 2 to about 4 wt. % of the mixture.

The following non-limiting example further illustrates the invention.

EXAMPLE 1

A door core of the present invention of the following composition can be manufactured from a mixture of the following ingredients:

Ingredients Amount (dry weight percent) Expanded perlite 70.19 Fast setting cementitious component 27.31 Comprising a mixture of Portland Cement and a Pozzolan Additive Polyvinyl alcohol 2 Glass Fibers 0.5

The fast-setting cementitious component constitutes a mixture of Portland cement (OPC) and either metakaolin or VCAS (PA) in a weight ratio of (OPC:PA) about 10.4:1.

Water in an amount of about 20-40 weight percent of the dry weight of the various ingredients should be added and the door core can be produced by pressing at about 150 psi and drying (curing) the pressed core at about 250° F. (120° C.) for about 4-5 hours.

It will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Unless otherwise specifically indicated, all percentages are by weight. Throughout the specification and in the claims the term “about” is intended to encompass + or −5%. 

1. A composition useful for producing a fire door core comprising an aqueous mixture of (A) expanded perlite and (B) a fast setting, cementitious component consisting essentially of (1) a hydraulic cement and (2) a pozzolan additive selected from the group consisting of (i) metakaolin, (ii) vitreous calcium aluminosilicate and (iii) mixtures thereof, which composition can be molded and shaped into a fire door core, and wherein, on a water-free basis, the expanded perlite (A) comprises about 65 to about 85 weight percent of the aqueous mixture, the fast-setting cementitious component (B) comprises about 15 to about 40 weight percent of the aqueous mixture, the organic binder (C) comprises about 1 to about 5 weight percent of the aqueous mixture and the fibrous reinforcement (D) comprises about 0.2 to about 1 weight percent of the aqueous mixture.
 2. The composition of claim 1 wherein the hydraulic cement is Portland cement and the Portland cement and the pozzolan additive are present in the fast setting cementitious component in a weight ratio within the range of 3:1 to 30:1.
 3. The composition of claim 2 containing an organic binder.
 4. The composition of claim 3 wherein the Portland cement and the pozzolan additive are present in the fast setting cementitious component in a weight ratio within the range of 4:1 to 15:1.
 5. A building material composition useful as a fire door core, comprising a cured aqueous mixture of (A) expanded perlite, (B) a fast setting, cementitious component consisting essentially of (1) a hydraulic cement and (2) a pozzolan additive selected from the group consisting of (i) metakaolin, (ii) vitreous calcium aluminosilicate and (iii) mixtures thereof, (C) an organic binder and (D) a fibrous reinforcement, which aqueous mixture before curing can be molded and shaped into a fire door core, and wherein said aqueous mixture contains on a dry weight basis about 65 to about 85 weight percent of the expanded perlite (A), about 15 to about 40 weight percent of the fast-setting cementitious component (B), about 1 to about 5 weight percent of the organic binder (C), and about 0.2 to about 1 weight percent of the fibrous reinforcement (D).
 6. The building material of claim 5 wherein the hydraulic cement is Portland cement and the Portland cement and the pozzolan additive are present in the fast setting cementitious component in a weight ratio within the range of 3:1 to 30:1.
 7. The building material composition of claim 6 wherein the Portland cement and the pozzolan additive are present in the fast setting cementitious component in a weight ratio within the range of 4:1 to 15:1.
 8. The building material composition of claim 5 wherein said aqueous mixture contains from about 15 to about 60 percent by weight water based on the dry weight of components (A), (B), (C), and (D).
 9. A building material composition prepared by drying an aqueous mixture of (A) expanded perlite, (B) a fast setting, cementitious component consisting essentially of (1) a hydraulic cement and (2) a pozzolan additive selected from the group consisting of (i) metakaolin, (ii) vitreous calcium aluminosilicate and (iii) mixtures thereof, (C) an organic binder and (D) a fibrous reinforcement, wherein, on a water-free basis, the expanded perlite (A) comprises about 65 to about 85 weight percent of the aqueous mixture, the fast-setting cementitious component (B) comprises about 15 to about 40 weight percent of the aqueous mixture, the organic binder (C) comprises about 1 to about 5 weight percent of the aqueous mixture and the fibrous reinforcement (D) comprises about 0.2 to about 1 weight percent of the aqueous mixture.
 10. The building material composition of claim 9 wherein the hydraulic cement is Portland cement and the Portland cement and the pozzolan additive are present in the fast setting cementitious component in a weight ratio within the range of 3:1 to 30:1.
 11. A method for making a fire door core from an aqueous mixture of materials, which method comprises mixing water, expanded perlite, a fast setting cementitious component consisting essentially of a mixture of hydraulic cement and a pozzolan additive selected from the group consisting of metakaolin, vitreous calcium aluminosilicate and mixtures thereof, an organic binder and a fibrous reinforcement, wherein, on a water-free basis, the expanded perlite comprises about 65 to about 85 weight percent of the aqueous mixture, the fast setting cementitious component comprises about 15 to about 40 weight percent of the aqueous mixture, the organic binder comprises about 1 to about 5 weight percent of the aqueous mixture, and the fibrous reinforcement comprises about 0.2 to about 1 weight percent of the aqueous mixture, the water being present in an amount in excess of the stoichiometric amount needed to hydrate the fast setting cementitious component and sufficient to provide a damp mixture but less than an amount which would produce an aqueous slurry of the intermixed ingredients, placing a charge of the damp mixture in a pressure mold of slab form, applying sufficient pressure to the damp charge in the mold to compress the charge to about 25% to 33% of its original volume and maintaining the pressure until the compression strength of the compressed charge is at least about 50 psi and up to about 170 psi, removing the molded slab from the mold and thereafter drying the slab by heating it sufficiently to remove excess water, and forming a fire door core piece from the dried slab.
 12. The method of claim 11 wherein the hydraulic cement is Portland cement and the Portland cement and the pozzolan additive are present in the fast setting cementitious component in a weight ratio within the range of 3:1 to 30:1.
 13. The building material composition of claim 6 wherein the expanded perlite has a density of about 6.5 lb./cu. ft.
 14. The building material composition of claim 6 wherein the organic binder is polyvinyl alcohol.
 15. The building material composition of claim 14 in which the intermixed ingredients further include unexpanded vermiculite in an amount not greater than about 4 wt. % of the dry ingredients.
 16. The building material composition of claim 15 in which the intermixed ingredients further include clay in an amount not greater than about 4 wt. % of the dry ingredients. 